The present invention relates to plasterboard trimming tools in general, and more particularly to tools of this type which are capable of producing uninterrupted scoring cuts on the opposite sides of the plasterboard.
Plasterboard has been used in the building industry for many years if not decades and has gained widespread acceptance for its advantageous properties, such as excellent strength, easy handling and compatibility with other building materials. When using plasterboard, however, it is often necessary to cut the same down to size so as to properly fit the space available for its mounting on a support structure. The usual construction of plasterboard is that of a plate of gypsum or a similar substance which is covered, on both of its major surfaces, with layers of paper mass. Since gypsum is a rather brittle substance, the layers of paper mass not only protect the gypsum plate from being damaged during storage, transportation or handling, especially by the formation of indentations therein, but also impart a certain degree of resilience to the plasterboard so that the gypsum plate will not crack or disintegrate when subjected to impacts.
Because of the above-mentioned function of the paper or cardboard layers covering the gypsum plate, it has been realized a long time ago by people active in the building trade that it is not necessary to completely cut through the plasterboard when it is desired to remove a portion thereof, such as for the purpose of trimming the plasterboard to the desired size. Rather, it is sufficient to cut through the two covering layers, thereby destroying their resilient properties at the regions of the cuts, whereafter the portion of the plasterboard can be broken away from the remainder of the plasterboard by applying appropriately directed forces or torque thereto. Due to the brittleness of the material of the plate, a substantially clean break will be obtained in the plate in registry with the scoring cuts through the covering layers, without disintegration of either the broken-away portion, or of the remainder, of the plasterboard.
Based on this recognition, it is currently customary in the building trade to use an ordinary multi-purpose utility knife for producing the scoring cuts in the covering layers. This approach produces satisfactory results, provided that the two scoring lines or areas at the opposite sides of the plasterboard are in alignment with one another and exactly follow the desired courses, in most instances, straight lines. However, under the constraints of available time, many a construction worker will not take the pains to accurately measure and indicate the desired courses; rather, depending on his skill, the construction worker will resort to estimating the proper location of the scoring areas and to producing the scoring cuts without following a straightedge or a similar implement. The frequent result of this intended time-saving operation is a jagged edge face of the plasterboard, or the need for resorting to an additional levelling operation in which considerable amounts of excessive material are to be removed from the marginal portion of the plasterboard.
To remedy this situation, there has already been proposed a trimming tool including a tool holder carrying, in an opposite relation, a pair of rotatably mounted scoring discs provided at their peripheries with a plurality of spaced cutting teeth with externally facing cutting edges. During the operation of this trimming tool, the marginal portion of the plasterboard is received between the scoring discs and, during the movement of the trimming tool along the marginal portion of the plasterboard, the scoring discs are caused to rotate due to the engagement of the cutting teeth with the plasterboard, which causes the cutting teeth to penetrate into the plasterboard in the succession of their locations on the peripheries of the scoring discs. Since the cutting teeth, as mentioned before, are spaced from one another, in the circumferential directions of the respective scoring discs, they will produce interrupted scoring cuts on the opposite major surfaces of the plasterboard. Then, when it comes to breaking the marginal portion of the plasterboard away from the remainder of the plasterboard, the webs remaining between the individual cut areas will interfere with the breaking operation so that, once more, the edge face will be jagged. This, of course, is very disadvantageous.